INSALIVATION. 185 



of starch can be converted, so that to the chemical action of the 

 saliva must be assigned a greater importance than it has hitherto 

 held. 



Much of the starch not changed to sugar is changed to dextrin, 

 according to Cannon and Day, " and thus, since dextrin is not easily 

 fermented, the food is saved to the organism. The especial value 

 of this process lies in the fact that it occurs to the greatest degree 

 in the fundus, in which region the hydrochloric acid, inhibiting the 

 action of many of the organized ferments, does not, for some time, 

 make its appearance. 



" In the early stages of gastric digestion, if food has been prop- 

 erly masticated, the fundus serves chiefly for the action of the 

 ptyalin ; the pyloric portion, after a brief stage of salivary diges- 

 tion, is thereafter the seat of strictly peptic changes. Later, after 

 two hours or more, as the contents of the fundus become acid, the 

 food in the stomach, as a whole, is subjected to the action of proteo- 

 lytic fermentation." 



The experiments of Cannon on the movements of the stomach, 

 to which we shall refer in detail in considering the function 

 of that organ, demonstrate most conclusively that in the process 

 the conditions are most favorable for a relatively prolonged 

 action of ptyalin on starch; the principal condition being the 

 absence of movement in this part of the stomach, so that the 

 food remains here in an alkaline condition for a considerable 

 length of time. This action of the saliva for so long a time after 

 the entrance of the food into the stomach emphasizes the impor- 

 tance of thorough mastication and insalivation. 



Mechanical Office of Saliva. While the teeth are thoroughly 

 comminuting the food they are at the same time working saliva 

 into the interstices which they make between the particles of the 

 food. This process not only facilitates the chemical action of the 

 ptyalin, but it tends also to keep the particles separated, so that 

 when the food reaches the stomach the gastric juice may the more 

 readily permeate it and produce its characteristic action. Saliva 

 aids also in softening the food, thus enabling the process of deglu- 

 tition or swallowing more easily to be performed. The secretion 

 of the mucous glands of the mouth is of special importance in 

 this act, the mucus secreted being of a ropy consistency and 

 possessing great lubricating properties. Saliva is intimately con- 

 nected with the sense of taste. Only soluble substances are 

 sapid that is, excite the sense of taste. Insoluble substances 

 have no taste. It is for this reason, among others, that calomel 

 is such an excellent cathartic for children ; being insoluble, it is 

 tasteless, and they readily swallow it. Soluble substances not 

 already in a state of solution are dissolved by the^ saliva, and in 

 this condition excite the sense of taste. When in a febrile or 

 other state, in which the secretion of the saliva is greatly dimin- 



